During optimization we replace NULL with 0 for not null 
date{time} fields, so uset MODE_NO_ZERO_DATE flag for a while 
as we don't want to give extra warnings.


mysql-test/r/strict.result:
  Fix for bug #22824: strict, datetime, NULL, wrong warning
    - test result.
mysql-test/t/strict.test:
  Fix for bug #22824: strict, datetime, NULL, wrong warning
    - test case.
sql/item_cmpfunc.cc:
  Fix for bug #22824: strict, datetime, NULL, wrong warning
    - turn off MODE_NO_ZERO_DATE in order not to get extra warinings
      in the save_in_field().